Between 1985 and 1987, 5,070 randomly selected persons living in 6 central African countries (Cameroon, Central African Republic, Chad, Congo, Equatorial Guinea and Gabon) were checked for serological evidence of haemorrhagic fever. Rural and urban areas were studied, including ecoclimatic zones ranging from dry savana to tropical rain forest. Virus-reactive antibodies were found with all antigens tested, and the global prevalence of positive sera was distributed as follows: Crimean-Congo haemorrhagic fever virus, 0.22%; Rift Valley fever virus, 0.18%; Ebola virus, 12.40%; Marburg virus, 0.39%; Lassa virus, 0.06%; and Hantaan virus, 6.15%. A significant variation in antibody prevalence was observed within the study regions. Association between the viruses was not observed.